1. Field of the Invention
The present invention relates to a substrate for an ink jet recording head, a recording head using the substrate, a recording apparatus with the recording head, and a method of driving the recording head.
2. Related Backaround Art
Nowadays, various recording methods have been developed and are available. Of these methods, ink jet recording methods for performing recording by emitting an ink from emission ports in accordance with a recording signal are popularly used since the apparatus used in these methods can be easily rendered compact and generates low noise. Among these methods, a method using electro-thermal energy conversion elements for applying heat to an ink to cause a bubble forming phenomenon as emission energy generation elements for emitting an ink is preferably used.
An ink jet recording head of this type has an element substrate on which first resistor elements (ink emission resistor elements) as electro-thermal energy conversion elements, which are electrically connected to a function element for selectively driving a plurality of electro-thermal energy conversion elements for emitting an ink, as described above, and second resistor elements (temperature control resistor elements), which are arranged for adjusting the viscosity of the ink by controlling the temperature, and are not electrically connected to the function element, are formed.
When the resistance values of the first resistor elements formed on the element substrate suffer a variation in the manufacture, if a common driving voltage is applied to the respective heads, different amounts of heat are generated due to a variation in resistance value, resulting in different ink bubble forming phenomena. Thus, ink emission amounts become nonuniform in units of heads, or stable ink emission cannot often be attained. Therefore, the resistance values of the emission resistor elements of the respective heads must be measured by some method, and voltages corresponding to the measured resistance values must be applied to suppress emission amount nonuniformity. However, when the resistance value of the emission resistor element of each head is to be directly measured, a resistance value including the resistance value of the emission resistor element and that of the function element electrically connected thereto is undesirably measured. As a result, the resistance value of only the emission resistor element cannot be accurately measured.
For this reason, the present inventors measured the resistance value of the temperature control resistor element which was electrically independent from the function element formed in a similar manner to that of the emission resistor element, and calculated a sheet resistance value based on the measured resistance value of the temperature control resistor element, thus estimating the resistance value of the emission resistor element.
On the basis of the estimated resistance value, data for setting an appropriate driving signal for stable emission of an ink is stored as, e.g., 4-bit data in a memory circuit on a printed circuit board on a recording head. When the recording head which stores data of the driving electric power is mounted on a recording apparatus, a control circuit unit of the ink jet recording apparatus reads data stored in the recording head, and supplies a driving signal suited for driving the emission resistor elements to the recording head in accordance with the read data, thus achieving adjustment of ink emission in units of heads.
However, the above-mentioned temperature control resistor element has a resistance value smaller than that of the emission resistor element since it has a resistor shape satisfying L.sub.1 /W.sub.1 &gt;L.sub.2 /W.sub.2, W.sub.1 &lt;W.sub.2, and L.sub.1 &lt;L.sub.2 (W.sub.1 and L.sub.1 are respectively the width and length of the emission resistor element, and W.sub.2 and L.sub.2 are respectively the width and length of the temperature control resistor element), so as not to form a bubble in an ink upon driving of the temperature control resistor element.
As described above, since the resistance value of the temperature control resistor element is set to be lower than that of the emission resistor element, when the resistance value is measured using the temperature control element, it is difficult to sufficiently accurately estimate the resistance value of the emission resistor element, and hence, it is difficult to drive the head by applying an appropriate driving signal to the emission resistor element.
On the other hand, when data for setting an appropriate driving signal condition for stable emission of an ink is stored in, e.g., the memory circuit on the printed circuit board on the basis of the resistance value estimated from the temperature control resistor, as described above, the number of data to be able to be stored is limited to several bits (e.g., 4 bits) in terms of a space for arranging the memory circuit. For this reason, the setting range of driving electric power to be applied to the emission resistor element is undesirably widened. In such a case, it is difficult to supply an appropriate driving signal to the emission resistor element. In order to solve this problem and to store a larger number of storage data, a memory element (e.g., a ROM or the like) may be mounted on the printed circuit board, or a region for arranging the memory circuit may be widened. However, this results in an increase in cost or size of the recording head itself.
When an appropriate driving signal cannot be set for the ink emission resistor element, e.g., when a driving signal is set to be too low, ink emission becomes unstable, and the dot size of an ink droplet diminishes, resulting in deterioration of print quality. On the other hand, when driving electric power is set to be too high, since electric power exceeding required power is supplied to the emission resistor element, the service life of the emission resistor element is shortened, and reliability of the recording head is lowered, thus posing problems to be solved.